Phasing of lysozyme
crystals using co-crystallized barium ions was performed using
single-wavelength anomalous diffraction (SAD) method using Cu Kα radiation with in-house source of
data collection. As the ion binding sites vary with respect to the pH of the
buffer during crystallization, the highly isomorphic forms of lysozyme crystals
grown at acidic and alkaline pH were used for the study. Intrinsic sulphur
anomalous signal was also utilized with anomalous signal from lower occupancy
ions for phasing. The study showed that to solve the structure by SAD
technique, 2.8-fold data redundancy was sufficient when barium was used as an
anomalous marker in the in-house copper X-ray radiation source for data
collection. Therefore, co-crystallization of proteins with barium containing
salt can be a powerful tool for structure determination using lab source.